(1) Technical Field
The present disclosure relates to organic electroluminescence (EL) elements that use EL of organic material, and methods of manufacturing organic EL elements.
(2) Description of Related Art
Organic EL elements are self-luminous and therefore have a high visibility. Further, organic EL elements are completely solid-state elements and therefore have excellent impact resistance. For these reasons and others, in recent years, the use of organic EL elements in display devices is becoming popular.
Organic EL elements have at least a light-emitting layer between a pair of electrodes (anode and cathode). In many cases, in addition to a light-emitting layer, organic EL elements are configured to have a functional layer for supplying electrons to the light-emitting layer (electron transport layer, electron injection layer), and a hole injection layer, hole transport layer, etc., between the light-emitting layer and the cathode. When driven, a voltage is applied between the pair of electrodes, and light is emitted as the result of recombination of holes injected to the light-emitting layer from the anode and electrons injected to the light-emitting layer from the cathode. Material development is being undertaken to achieve high-efficiency light-emitting properties and low-voltage drive properties for such organic EL elements. For example, JP 2002-313581 proposes an organic EL element that has a low drive voltage and high electron transport properties, by using alkali metal salts as a doping agent for the light-emitting layer.
However, conventional organic EL elements have low light emittance efficiency, due to an imbalance in the amount of electrons and the amount of holes injected to the light-emitting layer.